We are investigating the regulation of the circadian rhythm of beta-hydroxy-beta-methyl glutaryl CoA (HMG-CoA) reductase in rat liver. Using antibody prepared after purification of the enzyme we hope to determine whether the rhythm is due to changes in synthesis and/or degradation of the enzyme and whether these mechanisms are altered by cholesterol feeding, fasting, and administering of certain hormones factors known to affect overall reductase activity. We are also studying the mechanisms involved in alteration of reductase levels in isolated rat hepatocytes incubated in the presence of lipoproteins or hormones.